Nature of Mind
Different systems emphasize one of three descriptions: the primordial
non-differentiated consciousness; the awakened state of mind which
is also universal; or the peaceful state of mind which is at rest,
in complete peace. The nature of mind can then be experienced
as blue, clear, or black aspects of consciousness. Each one of
these can be considered a state of the nature of the mind. But
we can say further that the nature of the mind is complete emptiness.
We can experience complete emptiness as non-differentiated consciousness
or as translucency, or as the night sky. There is always a subtle
consciousness that perceives emptiness. The subtle consciousness
can be restricted by your own personal consciousness, so that
you don't see it as it is, or it can be expanded completely. (Diamond
Heart Book 2, pg 23)

This, then, is one concept of the nature of mind: to think of
it as consciousness, as a capacity or the very nature or substance
of knowing. Without it there can be no knowing, no consciousness,
no perception. In the process of becoming identified with our
egos, however, we separate ourselves from it, and then we never
know it, we simply use it. When we relax the hold of the ego,
our individuality, we can have a sense of non-differentiated consciousness
in daily life. (Diamond Heart Book 2, pg 20)